US2508941A

US2508941A - Electronic timing circuit

Info

Publication number: US2508941A
Application number: US659994A
Authority: US
Inventors: John H England
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1946-04-05
Filing date: 1946-04-05
Publication date: 1950-05-23
Anticipated expiration: 1967-05-23

Description

y 5 J. H. ENGLAND 2,508,941

ELECTRONIC TIMING cmcurr Filed April 5, 1946 REC TIF/ER /N V E N To R 555"521255" JOHN'H ENGLAND REGULATOR Patented May 23, 1950 UN 1 TED STATES 508,941

ELECTRONiC TmflNGfClRCUIT Johnimlnglana, Welleslei-Hills, assigfloi' toRaytheo'n Manufaoturing Company, N ew-ton,

Mass.,a corporation of Delaware Application AinilS, 194B,Serial'No. $9,991

:6 Claims. 1 This invention relates to electrical eireuitsend more particularly to an electronic timing c'irouit for electric welding equipment.

An object of this invention is to devise an electro'nio timing circuit for electric welding equipment in whioh there is no necess'it'y for a self biasing circuit or a separate external source of bias to block the rela tubes.

Another object is to devise a novel electronic timing oirouit in which the relay tubes are eon-'- trolled bya variation of their soreen'grid-potefrtials.

The foregoing and other'objects of the invem ion will be best understood from the following description of an exemplification thereoi, reference being had to the aecompanying drawing, wherein the single figure is a diagrammatiorep resentat ion oi one-means of-carryingout the inve ntlon.

In'the drawing; two pieces of'workitl are t ese to be welded with the system of this invention. These pieces are placed betweenupper and lower electrodes 46 and 4-8, respectively, of welding machine 43, "which electrodes are oonnecte'd to the terminals of secondary 51 of welding transformer 58. The primary 59 of said transformer is connected to the output terminals of a controlled energy supply system "6B, the input "terminals 9 and 15 of which are connected-to a source of 21- ternati g -current i. -Supp1ysystem 60 has two control terminals 6 'I and is arranged, in response to completion of a ei'rcuit 'betweenterminals =61, to supply electric current of a -predetermined value, for a predetermined-tune, to the primary 59 of welding transformer '58, and hence also to the electrodes '46 and -48, toiheat work '41 to'welding temperature. Electrode 46 is movable vertieally'to provide pres'sure on work 4-1 to force-the two pieces together with apredetermined force. Electrode 45 is meohanically connected t'o piston 45 mova-blein cylinder '44, said piston being moved upwardly or downwardly in responsefto the ad-*- mission of compressed air into said eyl'inder from supply 53 or high-pressure supply'st through Valves 52 or-SE-Whih are controlledhysolenoids 5! and 5-4, respectively. Solenoid 5! so controls valve :52 that,-when saidjsolenoid is ener'giied, valve 52 will be operatedtoadmit air iromsupply 53 to the upper portion of cylinder 44, moving piston 45 and electrode 46 downwardly, While when said solenoid is deenergizedvaive 52'Wi1lbe operated to admit air rrom'said sljlji 'ply to the lower portion of tlyl-irid'e'r 44,-movingpiston 45am electrode 46 upwardly. Solenoid s4, -=energ'ized, opens valve 55 if; "admit air from high downwardly.

pressure sup ly S6 to th upper portlonof cylilr- 'der '14, moving iston 45 and electrode 46 elown ward'ly with increased pressure-against 'work ii.

In welding with the system of this invention, the upper electrode must be forced against the woman-e1 then the Welding c'urlent applied'to the Work toheatit t'o we uing'temperature. A o rtain time after the Welding current has heenapplied, while the welding eurrent still "on and when the wen; h s been heated-to a predeten mined temperature, a forging pressure'must he a plied to force the 'pl ecesof; work together under an increased pressure. This requires atimine eiroui-ttotimethe period between the afifilicaffibh of thewelding current and the appl i'eationof the forging pressure. -A eertain' time after the forg ing pressure has been applied, the forging pres-- su-re must be released and the upper electrode moved away hem the work, whieh requires "a Second timing Circuit for this interval between the 'application of the forging pressure and the release of the forging pressure. A'third time in:- terval must be provided forthe proper-releas d the forgi-ngpressurehefore the system is reset for the next operatioi-l -which requires a third tithing circuit to establish-this interval.

The source of alternatingourrent i is eonhe'eted to supply a re'otifi er B3-and'a1so a rectifier, filter, and voltage re ulator 2 Rectifier 2 is so arrangedthat between its output terminalse and 1 there is a potential difierenee of 1 05 volts D. G,

"and-a difierenee of 220 volts D. between output Switch 62 is ordinarily foot-operated, and closure 0f the same will energize relays. bilhal ly bpl l contacts I 1 "0f r8133 Bare-connected ifislill'nt with .sw-iteh fiz, to provide a-holuing circuit to main tain relay 8 energizedia'fter it; has been fii'steher gi'zed by operation-or switch 62. seleneld'el connected in series Witrh normally-open contacts 13 Of relay 8 ECI'OSSSOHT'ELG i, S0 38 tO-b l'ilQiZEfl when relay contacts -f3- are closed by energization of relay- 8; When solenoids! 1S l 'lerg iied by (310* sure of contacts l3,valve 52 willbe opened-to sup l'yair rremsou rc e 53 into 'theupper end or e'ylin oer u rorem piston '45 and depereleetrode it Operating winding [6 of relay [4 is connected in series with resistor 64 and

contacts

49 and 50 across the source leads 6 and 4|.

Contacts

49 and 58 are arranged to be closed by a member carried by upper electrode 46, in such a Way that when upper electrode 46 has moved a predetermined distance, said contacts will be closed to complete a circuit through winding it of relay i4, energizing said relay. Operating winding 22 of relay is connected across source leads 6 and 4|, in series with normally-open contacts 19 of relay [4, and a resistor 65. Relay 29 is arranged to have a time delay between the time that it is energized and the time that its normally-open contacts 23 close, to insure that the application of welding current to the electrodes will be delayed somewhat to allow for the mechanical time delay of the electrode moving equipment. Contacts 23 of relay 20 are connected to control terminals 6| of the controlled energy supply system 60, in such a way that a circuit will be completed between said terminals 6i when relay 20 is energized. When relay 20 is energized, therefore, a welding current will be supplied to the

electrodes

45 and 48.

As stated above, a time interval must be provided between the application of the welding current and the application of the forging pressure. This time interval is established through the use of tube 66 and its associated circuit elements. The three time intervals, which, as stated above, are required for the exercise of this invention, are provided by tubes 6E, 61, and 68, respectively. These tubes, in cooperation with their associated circuit elements, provide the timing circuits. The operation of the fundamental timing circuit, consisting of tube 66 and its associated circuit elements, will now be described. Tubes 61 and G8, with their associated circuit elements, operate in essentially the same manner as this fundamental timing circuit. Tube 66 includes anode 69, screen grid 12, control grid 15, and cathode I8. Anode 59 is connected, through control winding 26 of relay 24 and resistor 8|, to lead 4!. Screen grid 12 is connected, through normally-open contacts ll of relay M, to lead 42. Cathode 13 is connected directly to common lead 6. Resistor 82, having a movable tap 83 thereon, is connected, in series with resistor 84 and with normally-closed contacts l8 of relay [4, across the source leads .42 and B. Movable tap 83 is connected, through condenser 85 and resistor 85, to control grid 15 of tube .65. Resistor 8'! is connected in shunt with condenser 85, while another circuit, comprising a resistor 89 and a switch 88 in series, is also connected in shunt with condenser 85. Since contacts ll of relay [4 are normally open, the screen grid 12 is floating, that is, it is not connected to anything. Under these conditions the tube 66 is non-conducting, since it has been found that when the screen grid of such a tube as 66 is free, the tube will be non-conducting. It has been found, also that when such a tube is in a conducting state, due to a sufiiciently small negative bias on the control grid and to a suincient positive potential on the screen grid, it may be rendered non-conducting by the mere removal of the positive potential from the screen grid. Originally, contacts I8 of relay I4 are closed, so that resistor 82 and tap 83 provide a potentiometer, the upper end of which is connected to the 105-volt lead 42 and the lower end of which, through resistor 84, is connected to the cathode 13. Originally, therefore, control grid 15 is positive relative to its cathode 18 when condenser 85 is discharged.

20 has caused the welding current to be supplied Grid or timing condenser will therefore be charged by means of grid rectification in tube 66, to a value of voltage depending on the setting of tap 83 on potentiometer 82, and will be maintained charged as long as contacts 18 are closed. Fixed resistance 84 is provided to limit the minimum charge on condenser 85. Condenser 85 is charged by grid rectification in such a direction that the potential of control grid 15 goes beyond plate current cut-off in the negative direction, that is, the potential of control grid 75 goes negative with respect to its cathode when the contacts l8 are opened.

Relay i4 is of the type in which, when it is ener- .gized, the normallyeclosed contacts [8 are opened slightly before the normally-open contacts I! are closed. When relay I4 is energized, contacts l8 are opened, thereby disconnecting the positive potential which was applied between the grid and the cathode, driving the grid 75 negative with respect to cathode l8 and also disconnecting the source which keeps condenser 85 charged, so that it begins to discharge through shunt resistor 81, thereby reducing the negative bias on control grid 15. When contacts I! of relay [4 are closed due to energization of said relay, the screen grid circuit is closed so that a positive potential of volts is applied to screen grid 12. However, this merely tends to cause tube 66 to conduct, and it will not conduct suflicient current to operate relay 24 in its plate circuit until the condenser 85 is discharged suificiently to reduce the negative bias on control grid 15 to the proper low value. It will be observed that the condenser voltage is the only voltage present in the control grid circuit after the normally-closed contacts i8 open.

With the values of the condenser 85 and discharge resistor 81 fixed, the time interval between the energization of relay I4 and the energization of relay 24 is determined by the position of tap 83. Other timing values can be secured by changing the values of condenser 85 and discharge resistor 81. By means of switch 88 and resistor 89 across the timing condenser 85, two ranges of timing can be secured.

When relay I4 is deenergized, contacts 11 are opened to remove the screen grid voltage from tube 66, rendering it non-conducting and deenergizing relay 24 in its plate circuit. Contacts 18 are closed when relay I4 is deenergized, to again connect the source to condenser 85, thereby again charging it and maintaining it charged by means of grid rectification in tube 66, and thus preparing the timing circuit for another operation.

Solenoid 54 is connected, in series with normally-open contacts 29 of relay 24 and normallyopen contacts 12 of relay 8, across the D. C. output of rectifier 63. Therefore, when relay 24 is energized at the end of the time interval above mentioned, solenoid 54 will be energized due to the closure of contacts 29 of relay 24 and due to the prior closure of contacts l2 of relay 8, which has previously been energized and which is maintained energized by its holding circuit comprising contacts H thereof. When solenoid 54 is energized, valve 55 will be opened to allow air from high-pressure air supply 56 to be admitted to the upper end of cylinder 44, thereby forcing piston 45 and upper electrode 46 downwardly with an increased pressure.

This increased pressure istermed the forging pressure. Prior to the application of this increased pressure, closure of contacts 230i relay ates-vii from system cu m the welding electrodes 4e and 48., thereby heatingwork 4'1.

A second timing circuit; consisting oftube 61' and its associated circuit elements, is provided to determine a time interval between the application of the forging pressure and the release of. the. forging pressure and of the initial pressure provided by the energization of solenoid 5i upon-the work. Tube 61 includes an anode 15, a screen grid #3, control grid Hi, and a cathode 79, said cathode being connected to common lead 6 or the system. Anode 10 is connected, throughcontrol winding-32 of relay ac and-a resistor 90 to lead 4!. Screen grid 13 isconnected, through normally-open contacts 21' ofre'lay 24, to lead-42. A series circuit, comprising normally-closed con-- tactsa28 of relay 24;, aresistor 9ihaving a movable tap 82 ther'eon,.and a. resistor 93, isconnected acrossileads. 6 and 42 of the system. Screen grid I3 is also connected to lead 42 by" a circuit including, in series, normallyopen-contacts 33 of relay 30. and normally-closed. contacts 46 of relay 3'1.

Movable. tap $2: is connected, through condenser 54 andresistor 95, to control grid to of tube 61'. Resistor 3B. is.- connected in shunttocondenser 9 While a series circuit, comprisin resistor 98 and switch, 951,. is also; connected shunt to saidcondenser. The operation of. this. timing circuit is substantially the samezas. that of the; timing circult previously described, so the description will not be: repeated. A certain time after the energization. of relay 24 to open. its contacts 28 and. close. its contacts 21,, relay 3%]. will be energized due to the: fact. that tube. 61 is rendered conducting.

A third timing. circuit, consisting of tube 68: and its associated circuit elements, is provided. Tube 685 includes an anode. H, a. screen grid 14,. a. control grid Ti, and a cathode 89%, said cathode being connected to; common lead- 6 of the system. Anode H is connected, through. control windin 3.5" ofirelayfil: and a. resistor 99, to lead 4 t. Screen grid 14 iseconnected, through normally-open contacts 33 of relay 313, to lead 42. A series circuit, comprising. normally-closed contacts 34 of relay 3-0, a: resistor Hi0; having; a. movable tap l'lll thereon,v and a resistor- I02, is connected across leads 6; and t2... Movable tap llil. is connected, through 3:. condenser 19.3 and. a resistor L64, to control. grid ll- Connected across condenser N33: is a, resister lzlii. Also; connected acrosssaid: condenser 3:3: is: the series: combination. of a. switch I06 and a. resistor lll 'l. This timing. circuit operates;- substantially the same as the timing circuit 66,. etc hereinbeiore; described, so that the descrip-- tion. of the; operation will not be repeated. A certain time interval after the energization of relay 3a which closesits contacts 33 and opens its normally-closed contacts. 34, relay 31 will be: energized to openits'normally-closed contacts 40. It will. beseen: that: the shunt circuit from lead 42 to s reen grid 113:, through contacts. 400i relay 3 .1. and contacts 36. of. relay 3!], provides in effect a. holding. circuit, since it maintains a positive; screen. grid. potential on screen: grid 13, even thou h contacts 21- have previously been opened:

by the: deenergization of relay 26.. This shunticircuit will be maintained completed after the. energization' of. relay 310; and: the; closing: of its contacts 36, until the energization. of? relay 3'! andtheopen-ingorits:contacts-40;.

To; put; the systems'into-operation;root-operated switch; 6:2 is closed. This. causes. relay 8-: to be the operating winding 10 thereof, are normally closed. Closure of contacts t3- by the energization of relay '8 causes thezenerg-ization in turn of solenoid 5i, thereby admitting air to the upper end of cylinder 44 and moving piston 45 and upper electrode 48 downwardly on the work. When electrode 46 has moved downwardly-a certain distance, contacts as and 50 are closed, completing a circuit throughoperating winding It of relay I4 and energizing said relay. Closure of contacts 19 of relay [-4 causes, after a time delay, energization of relay 20, closing its contactszd, which completes a circuit between the two controlterminals Bl of supply system Gt, to supply welding current to the

electrodes

46 and 48. Energization or relay-l4 establishes the beginning of the time interval determined by'tube 66 and its associated circuit elements; at the end of which interval relay 2 4 is energized.

When relay 24 is energized, the closure of'it's contacts 29 completes a circuit to the forge solenoid 54, thereby controlling valve to admit air from the high-pressure air supply 56' to the upper end of cylinder 44, thereby forcing piston 45 and upper electrode 45 downwardiy' with the increased forging pressure.

Energization of relay 24 also begins the second time interval, determined by tube 61 and its asso-- ciatedcircuit elements, at the end of which interval relay'Ba is energized. Relay 24, as is alsothe case with relays I4and 30, establishes the beginning of the time interval by the opening of its contacts 28 which are in series with the grid potentiometer of the following tube, and by the closure or itscontactit-which are in series with the: potential source and the screen grid 13 of the following tube.

When relay 3 0 isenergized, normallymlosedcontacts 35 thereof willbe opened. Opening of contacts 35 will cause deenergizaluon of relay 8,- because said contacts are" in series with. the oper-- ating winding ill thereof. Opening: of contacts t3 of relay 8 will deenergize solenoid. 51, thereby admitting air to thelower end of. cylinder 44, and mOVing piston '45 and. upper electrode 46 upwardly. Opening of contacts I! of relay 8 will cause deenergization -of..solenoid 54, thereby closing. valve 55 and l'eleassingthe forging. pressure. When upper electrode so has travelled up-- wardly a certain distance, contacts 49 and50? will be separated, thereby deenergizing relay I l.- Deenergization of relay l4 by opening of its contacts l3, cause deenergization of relay 25. Deen-ergization of relay 2i will,v by opening of its contacts 23, reset the: control. circuit for' sup-- ply system 60.. When relay i4 isdeenergized,- opening of its contacts: i l will remove the posi-- tive: potential from screen grid l -2 or tube 65, thereby cutting on said tube and deenergizing relay 24. Closure of contacts t8 of; relay [4 recon meets the source to condenser 85, therebycom pleting the charging circuit for said' condenser.

Deenergization of tube-relay 24 causes opening of contacts; 2:1 and 29,.and'closure'oi contacts 28". Opening of contacts 21 tends torremov e theposi tive potential from screen 1.3, and would cut off tube: 61 and deenergizetuberelay 30 were it not for the shunt circuit including contacts 36-and 4!], which maintains the positive potential on screen 13 as long as said shunt circuit is completed. source to condenser 94, tending tostart recharging saidcondenser. Opening of. contacts 29, contacts [2 having already been opened,- prepares the, forge solenoid circuit-for the next operation.

energized. since: the contacts 35,. in. series. with m When-v thethird. time interval as set by the:

Closure of. contacts 25 reconnects the values of condenser I03, resistor I85 and/or I01, and by the position of tap H, has elapsed, tube relay 31 will be energized, thereby opening nor-, mally-closed contacts 40 thereof. Relay 31 will remain energized as long as positive potential is on screen grid 14 Of tube 68. The shunt circuit, including contacts 36 and 40, from the source to screen 73 of tube 61, is provided to insure that tube 67 will be maintained conducting, thereby maintaining relay 3i! energized, long enough to span the third time interval and allow energize.- tion of relay 37. Opening of contacts 40 will, assuming relay 24 has already been deenergized toopen contacts 21 (which is ordinarily the case) remove the positive potential from screen grid 13 of tube 61, thereby cutting off said tube to deenergize tube relay 30.

Deenergizatlon of relay 30 will cause opening of its contacts 33 and 36, and closure of its contacts 34 and 35. Opening of contacts 33 will remove the positive potential from screen grid H of tube 68, thereby cutting off said tube and deenergizing relay 3! to reclose contacts 40, thereby preparing said relay and the circuit controlled thereby for the next operation. Closure of contacts 34 will connect the source to timing condenser I03, completing a charging circuit therefor. Closure of contacts 35 will condition the energizing circuit of relay 8 for the next operation, while the opening of contacts 36 will condition the shunt circuit to screen I3 for the next operation. The next operation, as before, may thereafter be initiated by the closing of switch 62.

It will be seen that

tubes

66, 61, and 68, together with their respective associated circuit elements, provide the three separately adjustable time periods hereinabove referred to. The first time period, that produced in the input of tube 66, may be termed the forge delay time, since when relay 24 is energized at the end of this time period, the circuit to forge solenoid 54 is completed through contacts 29 of this relay. The second time period, that produced in the input of tube 61, may be termed the hold time, since at the end of this period relay 30 is energized to open contacts 35, deenergizing relay 8 and head solenoid to start moving the electrode 46 upwardly. The third time period, that produced in the input of tube 58, may be termed the reset time, since at the end of this period relay 3! is energized to open contacts 40, thereby resetting or deenergizing relays 3D and 31 in turn.

Of course, it is to be understood that this invention is not limited to the particular details described above, as many equivalents will suggest themselves to those skilled in the art. For example, if desired the screen grids of the tubes may be connected to their cathodes through resistors of high value rather than being left free. Various other variations will suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

' What is claimed is:

1. A timing circuit including, in combination, an electron discharge tube having at least anode, cathode, control grid and screen grid elements, a source of potential, means connecting the anode-cathode path of said tube in series with a device to be operated across said source, a condenser having one terminal connected to said control grid and its other terminal connected to an intermediate tap on a potentiometer across said source, whereby said condenser charges by grid rectification in said tube and whereby said control grid is biased negatively due to said condenser charge when said potentiometer is disconnected from said source, switching means operative at a predetermined instant to disconnect said potentiometer from said source and to thereby allow said condenser to discharge and switching means operable with said last-named means for applying a positive potential from said source to said screen grid to allow said tube to conduct.

2. A timing circuit including, in combination,-

an electron discharge tube having at least anode, cathode, control grid and screen grid elements, a source of potential, means connecting the anodecathode path of said tube in series with a device to be operated across said source, a condenser having one terminal connected to said control grid and its other terminal connected to an intermediate tap on a potentiometer across said source, whereby said condenser charges by grid rectification in said tube and whereby said control grid is biased negatively due to said condenser charge when said potentiometer is disconnected from said source, a discharge circuit across said condenser, a pair of normally-closed contacts connected in series with said potentiometer, means operative at a predetermined instant to open said contacts to disconnect said potentiometer from said source and to thereby allow said condenser to discharge through said discharge circuit, a pair of normally-open contacts connected in series with said source and said screen grid for applying a positive potential from said source to said screen grid, and means operative to close said last-named contacts.

3. A timing circuit including, in combination, an electron discharge tube having at least anode, cathode, control grid and screen grid elements, a source of potential, means connecting the anode-cathode path of said tube in series with a device to be operated across said source, a condenser having one terminal connected to said control grid and its other terminal connected to an intermediate tap on a potentiometer across said source, whereby said condenser charges by grid rectification in said tube and whereby said control grid is biased negatively due to said condenser charge when said potentiometer is disconnected from said source, a relay having at least a pair of normally-closed contacts and a pair of normally-open contacts, means connecting said normally-closed contacts in series with said potentiometer, means connecting said normally-open contacts in series with the positive lead of said source and said screen grid, and means for energizing said relay to open said normally-closed contacts and to close said normally-open contacts.

4. A timing circuit including, in combination, an electron discharge tube having at least anode, cathode, control grid and screen grid elements, a source of potential, means connecting the anode-cathode path of said tube in series with the device to be operated across said source,

.means for applying a negative potential to said control grid, means for causing said negative potential to decrease with time from a predetermined instant, and a switch operable with said last-named means for applying a positive potential from said source to said screen grid to allow said tube to conduct.

5. A timing circuit including, in combination, an electron discharge tube having at least anode, cathode, control grid and screen grid elements, a

source oi potential, means connecting the anode-- cathode path of said tube in series with a device to be operated across said source, a condenser connected to said control grid, a resistive circuit connected across said condenser, means for charging said condenser from said source by grid rectification in said tube, switching means operative at a predetermined instant for applying the condenser voltage alone across the control grid and cathode to bias said control grid negatively and for disconnecting said condenser from said source to allow said condenser to discharge through said resistive circuit, and switching means operable with said last-named means for applying a positive potential from said source to said screen grid to allow said tube to conduct.

6. A timing circuit including, in combination, an electron discharge tube having at least anode, cathode, control grid and screen grid elements, a source of potential, means connecting the anodecathode path of said tube in series with a device to be operated across said source, a condenser connected to said control grid, a discharge circuit connected across said condenser, a relay having at least a pair of normally-closed contacts and a pair of normally-open contacts, means connecting said normally-closed contacts in series with said source and said condenser for charging said condenser by grid rectification in said tube, means connecting said normally-open contacts in series with the positive lead of said source and said screen grid, and means for energizing said relay to open said normally-closed contacts and to close said normally-open contacts, the opening of said normally-closed contacts applying the condenser voltage alone across.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,292,846 Pritchard Aug. 11, 1942 25 2,347,826 Heisner May 2, 1944 2,364,680 Wolfner Dec. 12, 1944